The present invention is directed to reflectors for use in electromagnetic antenna systems, and, more particularly, to reflectors capable of reflecting electromagnetic signals having two or more frequencies.
In the communication field, a number of systems exist which require antenna systems to be capable of operating at two or more frequencies. For example, in military and commercial satellites systems, it is common for the uplink signal from a ground station to the satellite to have a first frequency while the downlink signal from the satellite to the ground station has a second frequency. Commercial and military Ka-Band communication satellites are one example of this where the uplink frequency is 20 GHz and the downlink frequency is 30 GHz.
In the past, communication satellites systems such as those mentioned above have handled the two frequencies by using reflector antenna systems in the satellites which are designed with an antenna feed (for example, a feed horn) and a reflector system (generally using a concave primary reflector and a sub-reflector). One technique in such systems has been to provide two antenna feeds with each one designed to shape the beam so that the uplink receiving beam of the satellite (for example, at 30 GHz) will have substantially the same beam width as the downlink transmitted beam from the satellite (e.g., at 20 GHz). Designing the feeds for this purpose is difficult, and they are sometimes not realizable within the practical constraints of the satellite environment. An alternative approach is to use a separate reflector for each frequency. This, of course, is not advantageous in a satellite system, given the limitations of size and weight which must be considered.